Data report · November 2026

Cost per email: Outlook vs SMTP cold email infrastructure

Compare cold email infrastructure on cost per email: the price of a mailbox divided by what it sends. In 31 days of one agency client running both side by side, an Outreach2day mailbox sent 3.35 cold emails a day and a Microsoft mailbox 1.49 (mailboxes in their first 14 days excluded from both), at the same reply rate per email. Per mailbox that is 2.2x the emails, 2.3x the human replies and 2.8x the interested replies.

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  • 46.37Mcold sends
  • 360,974sending mailboxes
  • 49,369sending domains
  • 4.21Mrecipient domains

On the Outreach2day platform, October 5 to November 3, 2026

Max Korolev
Max KorolevFounder & CEO, Outreach2day
Published November 4, 2026

Same agency client, 31 days, mailboxes aged 14+ days

Cold emails a mailbox sends a day

  • Outreach2day mailbox3.35
  • Microsoft mailbox1.49
Per email at $2.50 a mailbox, ours
$0.0249
The same $2.50 on a Microsoft mailbox
$0.0559

Key findings

Ten findings, each with its sample and period

Every finding is one sentence with its number, unit, sample and period. Link to it by its number, or copy the citation line under it.

  1. 01

    An Outreach2day mailbox sent 3.35 cold emails a day and a Microsoft mailbox 1.49, 2.2 times as many emails per mailbox, so the same price per mailbox buys 2.2 times as many emails.

    n: 24.00M and 33.73M sends from an average of 231,297 and 729,281 mailboxes a day; one agency client running both side by side, anonymised, October 4 to November 3, 2026, mailboxes in their first 14 days excluded from both pools

  2. 02

    A Microsoft mailbox has to cost less than $1.11 a month to match a $2.50 Outreach2day mailbox on cost per email ($2.50 × 1.49 ÷ 3.35).

    n: Arithmetic on finding 1; $2.50 is the Outreach2day list price per mailbox a month

  3. 03

    In 8 of 8 workspaces that run both, Outreach2day mailboxes sent more emails per mailbox than Microsoft mailboxes: 3.67 against 1.42 a day pooled, 2.6 times as many.

    n: 8 workspaces, 43.0M sends from an average of 377,905 Outreach2day mailboxes a day; one agency client running both side by side, anonymised, October 4 to November 3, 2026, all mailboxes in the account

  4. 04

    Per mailbox, Outreach2day mailboxes earned 2.3 times the human replies of Microsoft mailboxes: 12.01 against 5.29 per 1,000 mailbox-days, or 0.36 against 0.16 a mailbox a month; counting all mailboxes in the account, ours were ahead in 7 of 8 shared workspaces.

    n: 86,120 and 119,687 human replies (auto-replies and bounces excluded); one agency client running both side by side, anonymised, October 4 to November 3, 2026, mailboxes in their first 14 days excluded from both pools

  5. 05

    Per mailbox, Outreach2day mailboxes earned 2.8 times the interested replies of Microsoft mailboxes: 0.39 against 0.14 per 1,000 mailbox-days.

    n: 2,830 and 3,120 replies labelled interested; one agency client running both side by side, anonymised, October 4 to November 3, 2026, mailboxes in their first 14 days excluded from both pools

  6. 06

    To Google Workspace recipients, Outreach2day mailboxes got 0.37% human replies per contacted lead and Microsoft mailboxes 0.20%, 1.85 times as many.

    n: 10,674,645 and 4,599,980 contacted leads; campaigns differ between the two mailbox pools; one agency client running both side by side, anonymised, October 4 to November 3, 2026, all mailboxes in the account

  7. 07

    To Microsoft 365 recipients, Outreach2day mailboxes got 0.012% interested replies per contacted lead and Microsoft mailboxes 0.007%, 1.7 times as many on small absolute rates.

    n: 24,612,001 and 22,463,036 contacted leads; one agency client running both side by side, anonymised, October 4 to November 3, 2026, all mailboxes in the account

  8. 08

    Per email, the human reply rate to Microsoft 365 recipients was the same from both kinds of mailbox, 0.38%: the gap per mailbox comes from emails per mailbox (2.2 times as many, finding 1).

    n: 24,612,001 and 22,463,036 contacted leads; one agency client running both side by side, anonymised, October 4 to November 3, 2026, all mailboxes in the account

  9. 09

    0.39% of emails from Outreach2day mailboxes bounced, against 0.63% from Microsoft mailboxes.

    n: Bounced ÷ sent on 24.00M and 33.73M sends; one agency client running both side by side, anonymised, October 4 to November 3, 2026, mailboxes in their first 14 days excluded from both pools

  10. 10

    56.4% of cold email sent from the Outreach2day platform went to Microsoft 365 inboxes, and Microsoft 365 recipients had the highest human reply rate of the major recipient providers, 0.473%.

    n: 46,369,695 cold sends; 22.6M Microsoft 365 contacts and 106,980 human replies; recipient provider by MX record; October 5 to November 3, 2026

The formulas

Compare infrastructure on cost per email and per reply

Price per mailbox says little until you divide it by what the mailbox sends. Four formulas, worked with the measured volumes: Outreach2day at its $2.50 list price, Microsoft 365 at a reseller's price.

  • Cost per email

    cost per emailequalsprice per mailbox a month divided by emails per mailbox a day × 30

    Outreach2day$2.50 ÷ (3.35 × 30) = $0.0249
    Microsoft 365$3.00 ÷ (1.49 × 30) = $0.0671

  • Cost per human reply

    cost per human replyequalsprice per mailbox a month divided by human replies per mailbox a month

    Outreach2day$2.50 ÷ 0.360 = $6.94
    Microsoft 365$3.00 ÷ 0.159 = $18.90

  • Cost per interested reply

    cost per interested replyequalsprice per mailbox a month divided by interested per 1,000 mailbox-days × 30 ÷ 1,000

    Outreach2day$2.50 ÷ (0.39 × 30 ÷ 1,000) = $213.68
    Microsoft 365$3.00 ÷ (0.14 × 30 ÷ 1,000) = $714.29

  • Emails per $1,000 a month

    emails per $1,000equals1,000 divided by cost per email

    Outreach2day1,000 ÷ $0.0249 = 40,200
    Microsoft 3651,000 ÷ $0.0671 = 14,900

The break-even price of a Microsoft mailbox

break-evenequalsour pricetimesMicrosoft rate divided by our rate

Below this price a Microsoft mailbox costs less per email or per reply than ours; above it, more. The rate is emails a mailbox sends a day, or replies per 1,000 mailbox-days.

To match oursAt $2.50At $0.50 (from 1,000)
per email1.49 ÷ 3.35 emails a day$1.11$0.22
per human reply5.29 ÷ 12.01 per 1,000 mailbox-days$1.10$0.22
per interested reply0.14 ÷ 0.39 per 1,000 mailbox-days$0.90$0.18

Cost table

What one email and one reply cost on each kind of mailbox

Each price divided by what that kind of mailbox sent in the panel: Outreach2day mailboxes at 3.35 emails a day and 0.36 human replies a month, Microsoft mailboxes at 1.49 and 0.16. Mailbox line only; the next section adds the sequencer.

  • Outreach2day

    List price, up to 99 mailboxes

    Price a mailbox a month
    $2.50
    Emails a mailbox a day
    3.35
    Cost per email
    $0.0249
    Per 1,000 emails
    $24.88
    Per human reply
    $6.94
    Per interested reply
    $213.68

  • Outreach2day

    Volume price from 100 mailboxes

    Price a mailbox a month
    $1.50
    Emails a mailbox a day
    3.35
    Cost per email
    $0.0149
    Per 1,000 emails
    $14.93
    Per human reply
    $4.16
    Per interested reply
    $128.21

  • Outreach2day

    Volume price from 1,000 mailboxes

    Price a mailbox a month
    $0.50
    Emails a mailbox a day
    3.35
    Cost per email
    $0.00498
    Per 1,000 emails
    $4.98
    Per human reply
    $1.39
    Per interested reply
    $42.74

  • Microsoft

    Exchange Online (Plan 1), Microsoft's list price, paid yearly

    Price a mailbox a month
    $4.00
    Emails a mailbox a day
    1.49
    Cost per email
    $0.0895
    Per 1,000 emails
    $89.49
    Per human reply
    $25.20
    Per interested reply
    $952.38

  • InboxKit

    Microsoft 365 mailbox, monthly

    Price a mailbox a month
    $3.00
    Emails a mailbox a day
    1.49
    Cost per email
    $0.0671
    Per 1,000 emails
    $67.11
    Per human reply
    $18.90
    Per interested reply
    $714.29

  • Hypertide

    Entra (Azure-hosted Outlook) inbox; $25 a domain of 25

    Price a mailbox a month
    $1.00
    Emails a mailbox a day
    1.49
    Cost per email
    $0.0224
    Per 1,000 emails
    $22.37
    Per human reply
    $6.30
    Per interested reply
    $238.10

  • InboxKit

    Azure-tenant mailbox, 100 to a tenant; $30 a tenant of up to 100

    Price a mailbox a month
    $0.30
    Emails a mailbox a day
    1.49
    Cost per email
    $0.00671
    Per 1,000 emails
    $6.71
    Per human reply
    $1.89
    Per interested reply
    $71.43
Cost per 1,000 emails, mailbox line, at measured volume
  1. Outreach2day, $0.50Outreach2day, $0.50: $4.98
  2. InboxKit, $0.30InboxKit, $0.30: $6.71
  3. Outreach2day, $1.50Outreach2day, $1.50: $14.93
  4. Hypertide, $1.00Hypertide, $1.00: $22.37
  5. Outreach2day, $2.50Outreach2day, $2.50: $24.88
  6. InboxKit, $3.00InboxKit, $3.00: $67.11
  7. Microsoft, $4.00Microsoft, $4.00: $89.49

Microsoft 365 seats. At $3.00 from a reseller or $4.00 from Microsoft, a Microsoft mailbox sending 1.49 a day costs $0.0671 to $0.0895 an email, 2.7 to 3.6 times an Outreach2day mailbox at its $2.50 list price.

Azure-tenant mailboxes. At $0.30 a mailbox in a full tenant of 100, the mailbox line alone costs less per email than ours at $2.50 or $1.50. From 1,000 mailboxes at $0.50 ours costs less, and once the sequencer an Azure mailbox needs is added, ours costs less at 100 mailboxes too (worked examples below). A full tenant of 100 is also the setup Microsoft's tenant limit hits hardest.

Sources, checked November 4, 2026: Outreach2day pricing; Outreach2day volume price on the comparison pages; Microsoft: Exchange Online plans; InboxKit pricing; Hypertide pricing. USD, monthly billing unless the row says otherwise. Volume prices are the ones on the comparison pages; larger volumes on the Enterprise plan.

Worked examples

100 and 1,000 mailboxes for a month, all-in

Each setup at its measured volume for 30 days. Mailbox-only offers get the cheapest Instantly plan that covers their emails, the rule our comparison pages use; Outreach2day includes warmup and its sequencer.

100 mailboxes

  • Outreach2day

    • Mailboxes100 × $1.50$150.00
    • Warmup and sequencerincluded$0

    Total a month$150.00

    Emails a month
    10,050
    Human replies a month
    36
    Cost per email
    $0.0149
    Cost per human reply
    $4.16
    Cost per interested reply
    $128.21

  • Microsoft 365 mailboxes (InboxKit)

    • Mailboxes100 × $3.00$300.00
    • Sequencer: Instantly Growthup to 5,000 emails a month$47.00

    Total a month$347.00

    Emails a month
    4,470
    Human replies a month
    15.9
    Cost per email
    $0.0776
    Cost per human reply
    $21.87
    Cost per interested reply
    $826.19

  • Azure-tenant mailboxes (InboxKit)

    • Tenants1 × $30.00, up to 100 mailboxes each$30.00
    • Sequencer: Instantly Growthup to 5,000 emails a month$47.00

    Total a month$77.00

    Emails a month
    4,470
    Human replies a month
    15.9
    Cost per email
    $0.0172
    Cost per human reply
    $4.85
    Cost per interested reply
    $183.33

1,000 mailboxes

  • Outreach2day

    • Mailboxes1,000 × $0.50$500.00
    • Warmup and sequencerincluded$0

    Total a month$500.00

    Emails a month
    100,500
    Human replies a month
    360.3
    Cost per email
    $0.00498
    Cost per human reply
    $1.39
    Cost per interested reply
    $42.74

  • Microsoft 365 mailboxes (InboxKit)

    • Mailboxes1,000 × $3.00$3,000.00
    • Sequencer: Instantly Hypergrowthup to 125,000 emails a month$97.00

    Total a month$3,097.00

    Emails a month
    44,700
    Human replies a month
    158.7
    Cost per email
    $0.0693
    Cost per human reply
    $19.51
    Cost per interested reply
    $737.38

  • Azure-tenant mailboxes (InboxKit)

    • Tenants10 × $30.00, up to 100 mailboxes each$300.00
    • Sequencer: Instantly Hypergrowthup to 125,000 emails a month$97.00

    Total a month$397.00

    Emails a month
    44,700
    Human replies a month
    158.7
    Cost per email
    $0.00888
    Cost per human reply
    $2.50
    Cost per interested reply
    $94.52

Emails a month = mailboxes × emails a mailbox a day × 30; replies a month = mailboxes × replies a mailbox a month. Domains are left out of every row: they are included with the Azure-tenant price and paid yearly on ours and on Microsoft 365.

Calculator

Put your own prices and volumes in

Start from a measured row or type the numbers from your own sending. Both setups use the formulas above.

Setup A

USD

Actual sends, every day

Without auto-replies

Cost per email
Cost per 1,000 emails
Cost per human reply
Emails per $1,000 a month

Setup B

USD

Actual sends, every day

Without auto-replies

Cost per email
Cost per 1,000 emails
Cost per human reply
Emails per $1,000 a month

Setup B costs 2.7x as much per email and 2.7x as much per human reply as setup A.

The data

One agency client, both kinds of mailbox, the same 31 days

12 workspaces of one agency client, anonymised; 8 of them ran Outreach2day and Microsoft mailboxes at the same time. Per-mailbox numbers leave out mailboxes in their first 14 days on both sides. Campaigns differ between the pools, so read the per-mailbox numbers together with the per-email ones.

  • Cold emails a mailbox a day

    2.2x
    • Outreach2day3.35
    • Microsoft1.49

    24.00M and 33.73M sends

  • Human replies per 1,000 mailbox-days

    2.3x
    • Outreach2day12.0
    • Microsoft5.3

    86,120 and 119,687 human replies

  • Interested replies per 1,000 mailbox-days

    2.8x
    • Outreach2day0.39
    • Microsoft0.14

    2,830 and 3,120 interested replies

  • Bounce rate

    0.39%
    • Outreach2day0.39%
    • Microsoft0.63%

    Bounced ÷ sent, on the same sends

Workspaces running both where Outreach2day mailboxes sent more per mailbox, all mailboxes in the account (pooled 3.67 against 1.42 a day)

8 of 8

Workspaces where they also earned more human replies per mailbox (pooled 13.0 against 4.9 per 1,000 mailbox-days, 2.65x)

7 of 8

Microsoft mailboxes sent about 51% of their own daily limit

The client had set about 2.9 emails a day per Microsoft mailbox; they sent 1.49. In practice Microsoft mailboxes do not keep up with their schedule. We have no tenant age or bounce-code data, so this report does not attribute the gap to one cause.

Sender × recipient: replies per contacted lead, all mailboxes in the account

Per email to Microsoft 365 recipients, both kinds of mailbox got the same human reply rate, 0.38%. Ours got more interested replies there and more human replies from Google Workspace recipients.

SenderTo Microsoft 365 recipientsTo Google Workspace recipients
Outreach2day mailboxes0.38%human · 0.012% interestedn = 24,612,0010.37%human · 0.015% interestedn = 10,674,645
Microsoft mailboxes0.38%human · 0.007% interestedn = 22,463,0360.20%human · 0.004% interestedn = 4,599,980

Human replies exclude auto-replies and bounces; interested = replies labelled interested; n = contacted leads, October 4 to November 3, 2026.

Why Microsoft mailboxes send less

Microsoft's sending limit is per tenant, and new tenants start at 10%

Microsoft caps external recipients per tenant over a rolling 24 hours at 500 × licenses^0.7 + 9,500 (Exchange Team Blog). Every mailbox in the tenant draws on that one pool, warmup and follow-ups included; once it is spent, external mail from every mailbox in the tenant bounces with 550 5.7.233.

Under MC1454397, published August 14, 2026 and rolling out from September 14 to the end of November 2026, a new tenant gets 10% of that quota for its first 30 days and 25% until day 60, and a trial tenant gets 500 a day. emailexpert called it a 60-day sending probation for new tenants; LazyAdmin walks through the new quotas.

A tenant that sends spam can also be blocked as a whole with 550 5.7.705, which stops mail from every mailbox in it until Microsoft Support lifts the block (Microsoft Learn). On October 14, 2026 Microsoft disabled more than 20,000 resold accounts of a phishing marketplace built on hijacked Microsoft 365 tenants (Microsoft); that action was against phishing, and it shows Microsoft acting against resold tenants at scale.

Our data shows the result in practice: Microsoft mailboxes in the panel aged 14 days and older sent 1.49 cold emails a day, about 51% of the 2.9 the client had scheduled. There is no tenant-age or bounce-code data in it, so the table puts Microsoft's formula next to the measured row and leaves the cause open.

tenant quota = 500 × licenses0.7 + 9,500 external recipients a day

External recipients per mailbox a day, warmup included, by tenant setup and tenant age
TenantDays 0 to 3010%Days 31 to 6025%Day 61 on100%
100 mailboxes, 1 licensequota 10,000 a day1025100
50 mailboxes, 1 licensequota 10,000 a day2050200
25 mailboxes, 1 licensequota 10,000 a day40100400
100 mailboxes, 100 licensesquota 22,059 a day2255221
25 mailboxes, 25 licensesquota 14,259 a day57143570
5 mailboxes, 5 licensesquota 11,043 a day2215522,209
Measured: Microsoft mailboxes in the panelcold sends only, mailboxes aged 14 days and older, every setup1.49 a day

External recipients per mailbox a day, warmup and follow-ups included, if every mailbox in the tenant sends the same amount. How Microsoft counts unlicensed or shared mailboxes is not documented. A dense tenant of 100 mailboxes on one license has 10 a mailbox in its first 30 days; after about 7 to 10 warmup emails, that leaves 0 to 3 cold emails a mailbox a day.

What operators and vendors report

Public posts from about 140 tracked cold email creators on LinkedIn and X and a Reddit archive of 45 subreddits (to June 10), May 1 to November 4, 2026: 42 hand-checked posts and comments from 36 authors say Microsoft banned, suspended, locked or blocked a sender's tenant or Microsoft mailboxes. That is 2 to 4 per 1,000 infrastructure posts from May to August and 10.1 per 1,000 in October, as MC1454397 rolled out. Google suspensions come up about as often in the same posts; most authors sell sending infrastructure.

Posts reporting Microsoft action against senders, per 1,000 infrastructure posts
  1. 2.3May 2026: 2.3 per 1,000
  2. 2.8Jun 2026: 2.8 per 1,000
  3. 4.2Jul 2026: 4.2 per 1,000
  4. 3.1Aug 2026: 3.1 per 1,000
  5. 5.9Sep 2026: 5.9 per 1,000
  6. 10.1Oct 2026: 10.1 per 1,000
  • An Azure inbox vendor reported that Microsoft blocked most mail from new tenants on their first two days, across 35,000+ accounts, October 31, 2026
  • Two Azure tenant vendors referred to an "azure ban wave last week" and "bans on the Azure tenants", November 3, 2026
  • An operator wrote an MC1454397 explainer because of "confusion today about Microsoft tenants getting blocked", October 30, 2026

Who you are emailing

Microsoft 365 recipients are the largest and best-replying segment

Microsoft-hosted inboxes were always the hard part of cold email. On the Outreach2day platform they took 56.4% of cold email and gave the highest human reply rate of the major recipient providers.

Share of cold sends by recipient provider56.4%

Microsoft 365Every other provider 43.6%

n = 46,369,695 cold sends, recipient provider by MX record, October 5 to November 3, 2026

Human reply rate of Microsoft 365 recipients0.473%

n = 22.6M contacted recipients and 106,980 human replies, October 5 to November 3, 2026. Replies to the last weeks of sends are still arriving, so the rate can rise slightly.

Methodology

How the numbers were measured

Platform. Sends from mailboxes on the Outreach2day platform, 2026-10-05 to 2026-11-04 (30 days): 46,369,695 cold sends from 360,974 mailboxes on 49,369 sending domains to 4.21M recipient domains. The recipient provider is classified by the MX record of the recipient domain. Human replies exclude auto-replies and bounces.

Panel. The per-mailbox comparison is one agency client running both kinds of mailbox side by side, anonymised: 12 workspaces, 8 of them with Outreach2day and Microsoft mailboxes at the same time, 2026-10-04 to 2026-11-03 (31 days). Microsoft mailboxes are the client's own Outlook, Microsoft 365 and Azure-tenant mailboxes from other vendors. Mailboxes in their first 14 days are excluded from both pools in the per-mailbox numbers, and so are sends from senders listed with no age; the workspace counts and the sender × recipient table have no age split and cover all mailboxes in the account. Campaigns differ between the mailbox pools, and both pools send what the client schedules, so emails per mailbox a day are actual sends at the limits the client set. Per-mailbox rates are the sum over days divided by mailbox-days. Interested replies are replies labelled interested.

Who publishes this. Outreach2day sells SMTP/IMAP mailboxes with warmup and a sequencer included; it sells no Microsoft 365 or Azure mailboxes. The Microsoft mailboxes in the panel are the client's own, bought from other vendors. Both pools include every mailbox the client ran in the window.

What the panel can and cannot show. Lists, copy and campaigns differ between the two pools, and the client sets the volume. The per-mailbox numbers are what the client got from each kind of mailbox in practice; per email, the human reply rate to Microsoft 365 recipients was the same, 0.38%.

Not in this report. Inbox placement, tenant ages and Microsoft bounce codes. Everything about Microsoft's limits comes from Microsoft's own posts and the trade press listed under Sources.

Reply rates of recipients count replies to sends in the window; replies to the last weeks were still arriving on November 4, 2026, so those rates can rise slightly.

Changelog

  • November 4, 2026: First edition: sends from October 4 to November 3, 2026, the cost formulas, the PDF and the CSV

How to cite this report

Plain text

Outreach2day, "Cost per Email: Outlook vs SMTP Cold Email Infrastructure (November 2026 Data)", November 2026. https://outreach2day.com/reports/cold-email-cost-per-email

APA

Korolev, M. (2026). Cost per email: Outlook vs SMTP cold email infrastructure (November 2026 data). Outreach2day. https://outreach2day.com/reports/cold-email-cost-per-email

The data is published under CC BY 4.0: reuse it, chart it and quote it, with a link to this page as the source. Each finding has its own link (#f1 to #f10).

PDF editionData (CSV)

Public sources on Microsoft's limits

  1. 1Microsoft 365 Message Center (public mirror). MC1454397, published August 14, 2026; rollout September 14 to the end of November 2026
  2. 2Microsoft Exchange Team Blog. Introducing Exchange Online Tenant Outbound Email Limits, the tenant quota formula
  3. 3Microsoft Learn. NDR codes 550 5.7.705 and 5.7.708, October 2, 2026
  4. 4emailexpert. Microsoft puts new Exchange Online tenants on 60-day sending probation, August 26, 2026
  5. 5LazyAdmin. Exchange Online tightens outbound limits for new, trial and EDU tenants, August 18, 2026
  6. 6Microsoft On the Issues. Disrupting the service economy behind transnational cybercrime operations, October 14, 2026

FAQ

Questions about the comparison

The objections we hear most, answered with the numbers above.

Azure-tenant mailboxes cost $0.30. Are they cheaper per email?

On the mailbox line, yes, against our list price. InboxKit sells Azure-tenant mailboxes at $30 a tenant of up to 100, $0.30 each when the tenant is full. At the measured 1.49 emails a day that is $0.00671 an email, below ours at $2.50 ($0.0249) and above ours at $0.50 from 1,000 mailboxes ($0.00498). With the sequencer an Azure mailbox needs, ours costs less per email in both worked examples: $0.0149 against $0.0172 at 100 mailboxes. A full tenant of 100 also splits one Microsoft quota: 10 external recipients a mailbox a day in its first 30 days, warmup included.

We run one tenant per domain. Does the tenant limit still matter?

Much less: a tenant of 5 licensed mailboxes has about 221 external recipients a mailbox a day even in its first 30 days. Cost per email still depends on what each mailbox actually sends, and Microsoft mailboxes in the panel sent 1.49 a day across every setup the client ran. One tenant per domain usually means a license per mailbox, $3.00 to $4.00 a month, which puts a Microsoft mailbox at $0.0671 to $0.0895 an email.

The reply rate per email is the same. Why does the mailbox matter?

Because you pay per mailbox. To Microsoft 365 recipients both kinds of mailbox got 0.38% human replies per contacted lead. An Outreach2day mailbox sent 2.2x the emails, so at that rate it brought 2.3x the human replies a month (0.36 against 0.16), and each reply cost less: $6.94 at $2.50 against $18.90 on a $3.00 Microsoft 365 mailbox.

Is it a fair comparison when the campaigns differ?

It is what one agency client got from both kinds of mailbox in the same 31 days. Because campaigns differ, the report also gives the per-email rates, the 8 workspaces that ran both (ours sent more per mailbox in 8 of 8 and earned more human replies per mailbox in 7 of 8) and a CSV with every aggregate.

Does Outreach2day sell Microsoft 365 or Azure mailboxes?

No. Outreach2day mailboxes are SMTP/IMAP mailboxes on your domains at $2.50 a month each from 12 mailboxes, with warmup and a sequencer included, or synced to Instantly and Smartlead. See pricing or the move off Microsoft 365.

Can I use these numbers in my own article or post?

Yes. The data is CC BY 4.0: quote it, chart it or reuse the CSV with a link to this page. Each finding has its own link (#f1 to #f10) and a ready citation line.

Full volume from day 14: 25 cold emails a mailbox a day

Add domains, create mailboxes and turn on warmup. You see every mailbox's warmup numbers from day one.

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